The present invention applies to the antiseismic protection of solid blocks, located in a building well and able to move with respect to the building if seismic waves arrive. It more particularly, but not exclusively, relates to an antiseismic supporting device for a pile block of a fast neutron nuclear reactor.
Nuclear reactors generally have to be protected against the prejudicial effects of earthquakes, which can produce more or less violent waves in the ground and whose horizontal and vertical components can, if no precautions are taken, have highly prejudicial, or even catastrophic effects on the devices used for supporting the pile block and on the different components thereof.
The present invention more particularly relates to fast neutron nuclear reactors, such as the French Superphenix reactor in Creys-Malville, in which the pile block is closed in its upper part by a concrete slab, which bears directly on the building of the reactor. In constructions of this type, the reactor vessel and the components of the pile block are suspended on said slab and extend into a well of the building structure.
In the case of the Creys-Malville Superphenix power station, the reactor building rests by its floor directly on the ground and is consequently subject to all the horizontal and vertical components thereof in the case of an earthquake. In order to improve this, it has already been proposed (EDF - SPIE Batignolles French Patent No. EN 75/20654 of 1.7.1975) that the reactor buildings be placed on fretted elastomer supports in order to reduce the effects of the horizontal components of seismic shocks. This method has already been used by Electricite de France for the pressurized water nuclear reactor in Cruas and, combined with sliding plates, in the pressurized water nuclear power station in Koeberg, South Africa.
These supports, which have a very considerable transverse flexibility, act in the horizontal plane in a manner of a filter, which only permits the passage of the frequency to which it is tuned. As the other frequencies have been eliminated, there is no longer any amplification of the movements of the oscillating path of the construction, which are then solely subject to the acceleration given by the spectrum of the ground for the tuning frequency.
The interest of such supports having a limited horizontal rigidity, but a high vertical rigidity, is to largely uncouple the horizontal vibration modes from the vertical vibration modes, so that in the case of horizontal excitation, the complete building virtually behaves as an oscillator with a single degree of freedom, which gives a horizontal translation movement which, in itself, absorbs 98% of the energy and almost completely eliminates the rocking movements. However, although the reduction in the stresses due to the horizontal components of the earthquake is spectacular, this device does not make it possible to reduce the influence of the vertical component.
In general, vertical stresses are less prejudicial (they only constitute a supplementary percentage to be added to the gravity) and it is easier to adapt thereto.
In the special case of fast neutron reactors, for which the pile block is suspended on the slab, the aforementioned procedures may in certain cases prove inadequate, because such reactors are very sensitive to vertical stresses.